You may have already spotted a couple fork-knife pairs in your travels around Fortnite. Since "fork-knife" sounds like "Fortnite", this is a running joke with Epic.

To find this particular set of cutlery you'll need to go to F8, between Salty Springs and Fatal Fields, right next to the Sky Platform.

Jump into the utensil-shaped caverns in the ground and start looking for a mine shaft. Once you've spotted that, you'll know you're in the right place. The area to search isn't very large, so this Fortbyte should be easy to find.